Grease composition

ABSTRACT

A calcium complex grease composition is disclosed. The grease composition has a high dropping point and a suitable thickness and is stable to heat.

PRIORITY CLAIM

The present application is the National Stage (§371) of InternationalApplication No. PCT/EP2012/073879, filed 28 Nov. 2012, which claimspriority from Japanese application no. 2011-259528, filed Nov. 28, 2011,the disclosures of which are incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a grease composition. Morespecifically, the present invention relates to a calcium complex greasecomposition containing a calcium complex soap having a high droppingpoint.

BACKGROUND OF THE INVENTION

As progress has been made in engineering technologies such as vehiclesand electrical equipment over the years, many types of equipment havebecome smaller, lighter and higher in output, and operating conditionshave increased in temperature and become harsher. As a result, greasesused in a variety of equipment have needed to exhibit improvedperformance at higher temperatures, and grease compositions having highdropping points and excellent thermal stability have been proposed.

Meanwhile, recent years have seen an increase in demand not only forimproved performance of greases at high temperatures, but also for humansafety during use and the use of materials having little environmentalimpact during production, and a grease that fulfils these requirementsis needed. Of these requirements, grease compositions that containlithium complex soaps, which are obtained by improving lithium soaps, orurea as thickening agents have high dropping points and exhibitexcellent heat resistance. Therefore, various proposals have been madefor these types of grease composition in order to further improve theseproperties.

As a grease composition that contains a lithium soap as a thickeningagent, JP 2006-131721 proposes a lithium complex grease which comprisesa lithium salt of an aliphatic monocarboxylic acid, a lithium salt of anaromatic dibasic acid and a lithium salt of an aliphatic dibasic acid,which has a higher dropping point than a lithium grease and which has awide range of usage temperatures. However, lithium, which is a rawmaterial of the lithium grease, is used in a wide variety ofapplications in addition to greases, and because there has been a highdemand for lithium recently, there are concerns that lithium resourceswill become depleted and the price of lithium will increase in thefuture. In addition, because the lithium complex grease involvesreacting two types of fatty acid in two stages, the production processof the lithium complex grease is complicated and requires a long periodof time.

In addition, as a grease composition that uses urea as a thickeningagent, JP 2008-231310 proposes a diurea grease able to be used at hightemperatures for a long period of time. However, amine compounds such asaniline, which are used as raw materials, are extremely toxic and mustbe handled with sufficient care during production, meaning that safetyis an issue.

As a result, grease compositions that use calcium as a thickening agent,which are superior in terms of safety, environmental burden andproduction costs, have been investigated as replacements for greasecompositions that use lithium soaps or urea as thickening agents, andcannot therefore be said to be satisfactory in terms of safety andenvironmental burden.

However, greases that use calcium soaps as thickening agents aregenerally inferior to lithium greases, lithium complex greases and ureagreases in terms of dropping point and heat resistance, and do nottherefore fulfil the recent requirements of greases.

Proposals have been made for greases known as calcium complex greases,which generally use a calcium complex soap of a higher fatty acid and alower fatty acid as a thickening agent, as greases that fulfil suchrequirements.

In particular, JP 2009-249419 proposes a calcium complex grease, whichuses calcium salts of a dibasic acid and a fatty acid as a thickeningagent, as a calcium complex grease having a high dropping point.However, in addition to the problem of being unable to maintain asuitable thickness if the added quantity of the thickening agent is low,this calcium complex grease is limited in terms of the form of thedibasic acid, and especially terephthalic acid, used as a raw material,and involves production problems such as requiring terephthalic acid tobe introduced at the high temperature of 120° C.

The problem to be addressed by the present invention is to provide acalcium complex grease which exhibits equivalent or superior heatresistance to a grease that uses a lithium soap or urea as a thickeningagent by maintaining (having or ensuring) a high dropping point andwhich can maintain a suitable thickness even if the quantity ofthickening agent is low.

SUMMARY OF THE INVENTION

The inventors found that it was possible to solve this problem by usinga calcium soap containing a specific higher fatty acid, a specific lowerfatty acid and a specific aromatic fatty acid. Accordingly, the presentinvention provides a grease composition containing a base oil and, as athickening agent, a calcium complex soap, wherein a substituted orunsubstituted straight chain higher mono-fatty acid having 18 to 22carbon atoms, an aromatic mono-fatty acid having a substituted orunsubstituted benzene ring and a straight chain saturated lowermono-fatty acid having 2 to 4 carbon atoms are used as fatty acids inthe calcium complex soap.

The grease composition may have a dropping point of at least 180° C. orhigher than this.

In addition, the grease composition may contain 2 to 15 parts by mass ofthe straight chain higher mono-fatty acid, 0.5 to 2 parts by mass of thearomatic mono-fatty acid and 1 to 5 parts by mass of the straight chainsaturated lower mono-fatty acid in terms of raw materials relative to100 parts by mass of the total blending quantity of the greasecomposition.

Moreover, said grease composition may be one in which the straight chainhigher mono-fatty acid is one or more fatty acids selected from amongstearic acid, oleic acid, 12-hydroxystearic acid and behenic acid, thearomatic mono-fatty acid is one or more fatty acids selected from amongbenzoic acid and para-toluic acid, and the straight chain saturatedlower mono-fatty acid is acetic acid.

Furthermore, a method for producing said grease composition may be onewhich includes a step of generating a calcium complex soap by adding thestraight chain higher mono-fatty acid, the aromatic mono-fatty acid, thestraight chain saturated lower mono-fatty acid and calcium hydroxide tothe base oil.

The calcium complex grease composition according to the presentinvention has a high dropping point and can maintain a suitablethickness even if the quantity of thickening agent is low, and cantherefore be used in high-temperature environments in which conventionallithium-based greases and urea greases cannot be used, and also achievesthe effect of being able to achieve safety, environmental properties andlow cost.

DETAILED DESCRIPTION OF THE INVENTION

The grease composition of the present aspect contains a “base oil” and a“thickening agent” as essential constituent components.

The base oil used in the grease composition of the present aspect is notparticularly limited. For example, mineral oils, synthetic oils andvegetable oils used in ordinary grease compositions, and mixturesthereof, can be used as appropriate. Specific examples thereof includeindividual or mixed base oils belonging to group 1, group 2, group 3,group 4 and so on in the base oil categories of the API (AmericanPetroleum Institute).

Group 1 base oils include paraffin-based mineral oils obtained bysubjecting a lubricating oil distillate, which is obtained byatmospheric distillation of crude oil, to an appropriate combination ofrefining means, such as solvent refining, hydrogenation refining ordewaxing. Group 2 base oils include paraffin-based mineral oils obtainedby subjecting a lubricating oil distillate, which is obtained byatmospheric distillation of crude oil, to an appropriate combination ofrefining means, such as hydrogenation refining or dewaxing. A group 2base oil, which is refined using a hydrogenation refining method such asa method used by Gulf and in which the total sulphur content is lessthan 10 ppm and the aromatic content is 5% or lower, can be preferablyused in the present invention. Group 3 base oils and group 2+ base oilsinclude paraffin-based mineral oils produced by subjecting a lubricatingoil distillate, which is obtained by atmospheric distillation of crudeoil, to a high degree of hydrogenation refining, base oils refined by anIsodewax process, in which waxes generated in a dewaxing process areconverted/dewaxed into iso-paraffins, and base oils refined by Mobil'sWax isomerisation process, and these can be preferably used in thepresent aspect.

Examples of synthetic oils include polyolefins, diesters of dibasicacids, such as dioctyl sebacate, polyol esters, alkylbenzenes,alkylnaphthalenes, esters, polyoxyalkylene glycols, polyoxyalkyleneglycol esters, polyoxyalkylene glycol ethers, polyphenyl ethers,dialkyldiphenyl ethers, fluorine-containing compounds(perfluoropolyethers, fluorinated polyolefins and the like) andsilicones. The abovementioned polyolefins include a variety of olefinpolymers and hydrogenated products thereof. It is possible to use anarbitrary olefin, and ethylene, propylene, butene, and α-olefins having5 or more carbon atoms and the like can be used. When producing apolyolefin, it is possible to use one of the abovementioned olefins or acombination of two or more types thereof. Polyolefins known aspoly-α-olefins (PAO) are particularly preferred, and these are group 4base oils.

Oils obtained from GTL (gas-to-liquid) processes, which are synthesisedby the Fischer Tropsch method of converting natural gas into liquidfuel, have a much lower sulphur content and aromatic content and a muchhigher paraffin component ratio than mineral oil base oils refined fromcrude oil, and therefore have excellent stability to oxidation andextremely low evaporative losses, and can therefore be preferably usedas the base oil in the present aspect.

The thickening agent used in the present aspect is a calcium complexsoap obtained by reacting a plurality of fatty acids with a specificbase (typically calcium hydroxide). The fatty acid sources for thecalcium complex soap according to the present aspect are (1) a higherfatty acid, (2) an aromatic fatty acid and (3) a lower fatty acid. Thefatty acid components (anionic components) of said calcium complex soapwill now be explained in detail.

(1) The higher fatty acid used in the present aspect is a straight chainhigher monocarboxylic acid having 18 to 22 carbon atoms. Here, saidstraight chain higher monocarboxylic acid may be unsubstituted or haveone or more substituent groups (for example hydroxyl groups and thelike). In addition, said straight chain higher monocarboxylic acid maybe a saturated fatty acid or an unsaturated fatty acid, but a saturatedfatty acid is preferred. Specific examples of saturated fatty acidsinclude stearic acid (octadecanoic acid, 18 carbon atoms),tuberuculostearic acid (nonadecanoic acid, 19 carbon atoms), arachidicacid (eicosanoic acid, 20 carbon atoms), heneicosanoic acid (21 carbonatoms), behenic acid (docosanoic acid, 22 carbon atoms) andhydroxystearic acid (18 carbon atoms, oil of hydrogenated castor oilfatty acid), and specific examples of unsaturated fatty acids includeoleic acid, linolic acid and linolenic acid (18 carbon atoms), gadoleicacid, eicosadienoic acid and mead acid (20 carbon atoms), and erucicacid and docosadienoic acid (22 carbon atoms). Moreover, it is possibleto use one of these fatty acids or a combination thereof. For example,when an unsaturated fatty acid is used, it is preferable to use theunsaturated fatty acid in combination with a saturated fatty acid.

(2) The aromatic fatty acid used in the present aspect is an aromaticmono-fatty acid having a substituted or unsubstituted benzene ring.Here, said aromatic mono-fatty acid may be unsubstituted or have one ormore substituent groups (for example, an o-, m- or p-alkyl group, ahydroxy group, an alkoxy group and the like). Specific examples thereofinclude benzoic acid, methylbenzoic acid (p-, m- or o-toluic acid),dimethylbenzoic acid (xylylic acid, hemellitic acid or mesitylenicacid), trimethylbenzoic acid (prehnitylic acid, durylic acid, or α, β-or γ-isodurylic acid), 4-isopropylbenzoic acid (cuminic acid),hydroxybenzoic acid (salicylic acid and the like), dihydroxybenzoic acid(pyrocatechuic acid, α-, β- or γ-resorcylic acid, gentisic acid orprotocatechuic acid), trihydroxybenzoic acid (gallic acid),hydroxy-methylbenzoic acid (p-, m- or o-cresotinic acid),dihydroxy-methylbenzoic acid (orsellinic acid), methoxybenzoic acid (p-,m- or o-anisic acid), dimethoxybenzoic acid (veratric acid),trimethoxybenzoic acid (asaronic acid), hydroxy-methoxybenzoic acid(vanillic acid or isovanillic acid) and hydroxy-dimethoxybenzoic acid(syringic acid). Moreover, it is possible to use one of these fattyacids or a combination thereof. Moreover, the alkyl groups and the alkylmoieties in the alkoxy groups in the “substituent groups” in the presentspecification are straight chain or branched chain alkyl groups having 1to 4 carbon atoms.

(3) The lower fatty acid used in the present aspect is a straight chainsaturated lower mono-fatty acid having 2 to 4 carbon atoms. Specificexamples thereof include acetic acid (2 carbon atoms), propionic acid (3carbon atoms) and butyric acid (4 carbon atoms). Of these, acetic acid(2 carbon atoms) is particularly preferred. Moreover, it is possible touse one of these fatty acids or a combination thereof.

Of these, from the perspectives of quality of texture, viscoelasticity(body), ease of production and so on, a combination of stearic acid asthe straight chain higher monocarboxylic acid, benzoic acid as thearomatic fatty acid and acetic acid as the lower fatty acid is mostpreferred.

In addition to the abovementioned calcium complex soap, it is possibleto additionally use another thickening agent in the grease compositionof the present aspect. Such other thickening agents include calciumtriphosphate, alkali metal soaps, alkali metal complex soaps, alkalineearth metal soaps, alkaline earth metals complex soaps (other than thecalcium complex soap), alkali metal sulfonates, alkaline earth metalssulfonates, other metal soaps, terephthalamate metal salts, clays,silica (silicon oxide) such as silica aerogels, and fluororesins such aspolytetrafluoroethylene, and it is possible to use one of these otherthickening agents or a combination of two or more types thereof. Inaddition, it is possible to use any other material able to impart athickening effect to a liquid substance.

Additives such as antioxidants, corrosion inhibitors, oil agents,extreme pressure additives, anti-wear additives, solid lubricants, metaldeactivators, polymers, metal-based detergents, non-metal-baseddetergents, anti-foaming agents, colourants and water repellency agentscan be added to the grease composition of the present aspect at a totaloptional component content of approximately 0.1 to 20 parts by massrelative to 100 parts by mass of the overall grease composition.Antioxidants include, for example, 2,6-di-t-butyl-4-methylphenol,2,6-di-t-butyl-paracresol, p,p′-dioctyldiphenylamine,N-phenyl-α-naphthylamine and phenothiazine. Corrosion inhibitors includefor example, paraffin oxides, metal salts of carboxylic acids, metalsalts of sulphonic acids, carboxylic acid esters, sulphonic acid esters,salicylic acid esters, succinic acid esters, sorbitan esters and avariety of amine salts. Oil agents, extreme pressure additives andanti-wear additives include, for example, zinc dialkyldithiophosphatesulphides, zinc diallyldithiophosphate sulphide, zincdialkyldithiocarbamate sulphides, zinc diallyldithiocarbamate sulphide,molybdenum dialkyldithiophosphate sulphides, molybdenumdiallyldithiophosphate sulphide, molybdenum dialkyldithiocarbamatesulphides, molybdenum diallyldithiocarbamate sulphide, organicmolybdenum complexes, olefin sulphides, triphenyl phosphate, triphenylphosphothionate, tricresyl phosphate, other phosphoric acid esters, andsulphurised oils and fats. Solid lubricants include, for example,molybdenum disulphide, graphite, boron nitride, melamine cyanurate, PTFE(polytetrafluoroethylene), tungsten disulphide, and graphite fluoride.Metal deactivators include, for example,N,N′-disalicylidene-1,2-diaminopropane, benzotriazole, benzimidazole,benzothiazole and thiadiazole. Polymers include, for example,polybutene, polyisobutene, polyisobutylene, polyisoprene andpolymethacrylates. Metal-based detergents include, for example, metalsulphonates, metal salicylates and metal phenates. Non-metal-baseddetergents include, for example, succinimide. Anti-foaming agentsinclude, for example, methylsilicone, dimethylsilicone, fluorosiliconesand polyacrylates.

An explanation will now be given of the blending quantities in thegrease composition according to the present aspect.

The blending quantity of the base oil is preferably 60 to 99 parts bymass, more preferably 70 to 97 parts by mass, and further preferably 80to 95 parts by mass, relative to 100 parts by mass of the overall greasecomposition.

The blending quantity of the calcium complex soap contained in thethickening agent is preferably 1 to 40 parts by mass, more preferably 3to 25 parts by mass, and further preferably 5 to 20 parts by mass,relative to 100 parts by mass of the overall grease composition.

The blending quantity of the higher fatty acid contained in the calciumcomplex soap is preferably approximately 0.5 to 22 parts by mass, morepreferably 1 to 18 parts by mass, and further preferably 2 to 15 partsby mass, relative to 100 parts by mass of the overall greasecomposition.

The blending quantity of the aromatic fatty acid contained in thecalcium complex soap is preferably 0.05 to 5 parts by mass, morepreferably 0.1 to 4 parts by mass, and further preferably 0.5 to 3 partsby mass, relative to 100 parts by mass of the overall greasecomposition.

The blending quantity of the lower fatty acid contained in the calciumcomplex soap is preferably 0.15 to 7 parts by mass, more preferably 0.5to 6 parts by mass, and further preferably 1 to 5 parts by mass,relative to 100 parts by mass of the overall grease composition.

The mass ratio of the base oil to the calcium complex soap is preferablybetween 99:1 and 60:40, more preferably between 97:3 and 70:30, andfurther preferably between 95:5 and 80:20.

The quantity of the higher fatty acid relative to 100 parts by mass ofthe total fatty acid content is preferably 62 to 70 parts by mass, morepreferably 64 to 69 parts by mass, and further preferably 65 to 68 partsby mass.

The quantity of the aromatic fatty acid relative to 100 parts by mass ofthe total fatty acid content is preferably 2 to 17 parts by mass, morepreferably 4 to 16 parts by mass, and further preferably 5 to 15 partsby mass.

The quantity of the lower fatty acid relative to 100 parts by mass ofthe total fatty acid content is preferably 10 to 24 parts by mass, morepreferably 11 to 20 parts by mass, and further preferably 12 to 17 partsby mass.

The mass ratio of the aromatic fatty acid relative to the higher fattyacid is preferably between approximately 97:3 and 70:30, more preferablybetween approximately 95:5 and 75:25, and further preferably betweenapproximately 92:8 and 78:22. If the proportion of the aromatic fattyacid exceeds 30%, a grease structure does not form, and if theproportion of the aromatic fatty acid is less than 3%, it is thoughtthat heat resistance will not be achieved.

The mass ratio of the lower fatty acid relative to the higher fatty acidis preferably between approximately 85:15 and 65:35, more preferablybetween approximately 82:18 and 70:30, and further preferably betweenapproximately 80:20 and 72:28. If the proportion of the lower fatty acidexceeds 35%, a grease structure does not form, and if the proportion ofthe aromatic fatty acid is less than 15%, it is thought that heatresistance will not be achieved.

The mass ratio of the lower fatty acid relative to the aromatic fattyacid is preferably between approximately 53:47 and 10:90, morepreferably between approximately 51:49 and 15:85, and further preferablybetween approximately 50:50 and 20:80. If the proportion of the lowerfatty acid exceeds 90 mass %, it is thought that the viscosity willdecrease and a grease structure will not form.

The grease composition of the present aspect can be produced using acommonly used grease production method. Although not particularlylimited, it is possible to, for example, place the base oil, higherfatty acid, lower fatty acid and aromatic fatty acid in a greaseproduction tank and melt the contents at a temperature of 60 to 120° C.Next, an appropriate quantity of calcium hydroxide dissolved ordispersed in advance in distilled water is introduced into theaforementioned tank. The fatty acids and the basic calcium (typicallycalcium hydroxide) undergo a saponification reaction, thereby graduallygenerating a soap in the base oil, and this is then heated so as tocomplete dehydration and form a grease thickening agent. Followingcompletion of the dehydration, the temperature is increased to 180 to220° C., blending is effected through vigorous stirring, and the mixtureis then allowed to return to room temperature. A homogeneous greasecomposition is then obtained by using a disperser (for example athree-roll mill).

The dropping point of the grease composition of the present aspect ispreferably 180° C. or higher, more preferably 210° C. or higher, furtherpreferably 250° C. or higher, and particularly preferably 260° C. orhigher. If the dropping point of the grease composition is 180° C. orhigher (which is at least 50° C. higher than that of an ordinary calciumgrease), it is thought that lubrication problems such as the possibilityof loss of viscosity at high temperatures, which can result in leakageor burning, can be suppressed. Moreover, dropping point means thetemperature at which the thickening agent structure is lost when thetemperature of a viscous grease is increased. Here, the dropping pointis measured in accordance with JIS K 2220 8.

In a thickness test, the grease of the present aspect preferably has athickness of No. 000 to No. 6 (85 to 475), more preferably a thicknessof No. 0 to No. 4 (175 to 385), and further preferably a thickness ofNo. 1 to No. 3 (220 to 340). Moreover, the thickness represents theapparent hardness of the grease. Here, the method for measuring thethickness can be one in which worked penetration is measured, inaccordance with JIS K 2220 7.

In a thin film heating test (150° C. for 24 hours), the greasecomposition of the present aspect exhibits an evaporation loss of lessthan 10%, preferably less than 7%, and more preferably less than 4%.Here, the method used in the thin film heating test is as follows. Asample weighing 3.0 g±0.1 g was coated on the central area portion (50mm×70 mm) of one surface of a test piece made from an SPCC steel sheet,as specified in the humidity test method of JIS K 2246, having athickness of 1.0 to 2.0 mm, a height of 60 mm and a width of 80 mm, andsubjected to a heating test at 150° C. for 24 hours, the weight of theSPCC steel sheet was measured before and after the heating test, and theevaporated quantity was determined from the formula below. Moreover, inthe thin film heating test, 0.5 parts by mass ofp,p′-dioctyldiphenylamine was added to 99.5 parts by mass of each of thegrease compositions disclosed in Working Examples 1 to 11 andComparative Examples 1 to 4, with the total blending quantity of thegrease composition being 100 parts by mass.Evaporated quantity (%)=(weight (g) prior to heating test−weight (g)following heating test)/(weight (g) prior to heating test)×100

If changes in the state (changes in colour, hardness and the like) ofthe grease following the thin film heating test are slight, thecomposition is good. The hardness of the grease prior to the test shouldbe maintained, the grease should not become fluid, and the appearance ofthe grease should be similar to that of the grease prior to the test ora pale brown colour.

The grease composition of the present aspect can of course be used incommonly used machinery, bearings, gears and the like, and can alsoexhibit excellent performance under harsher conditions, such as underhigh-temperature conditions. In vehicles, for example, the greasecomposition of the present aspect can be preferably used to lubricateengine peripherals such as starters, alternators and various actuators,propeller shafts, constant velocity joints (CVJ), wheel bearings,powertrain components such as clutches, electrical power steering (EPS),braking devices, ball joints, door hinges, handles, cooling fan motors,brake expanders and the like. Furthermore, the grease composition of thepresent aspect can also be used in construction equipment such as powershovels, bulldozers and cranes, and a variety of locations that aresubjected to high temperatures and high loads, such as the iron andsteel industry, the papermaking industry, forestry equipment,agricultural equipment, chemical plants, power stations, dryingfurnaces, copiers, railway vehicles and threaded joints for seamlesspipes. Intended uses include hard disc bearings, plastic lubrication andcartridge greases, and the grease composition of the present aspect canalso be preferably used in these intended uses.

EXAMPLES

The present invention will now be explained in greater detail throughthe use of working examples and comparative examples, but is in no waylimited to these examples.

The raw materials used in the working examples and comparative examplesare as follows. Moreover, if not explicitly disclosed, the quantitiesshown in Working Examples 1 to 11 and Comparative Examples 1 to 5 are asshown in Table 1 below. Moreover, the raw material quantities disclosedin Table 1 (especially those of calcium hydroxide and fatty acids) arethe quantities of the reagents. Therefore, the actual quantities of thecomponents in the composition are calculated on the basis of thenumerical values shown in Table 1 and the purities given below.

Thickening Agent Raw Materials

Calcium hydroxide: Special grade, purity 96.0%

Stearic acid: Special grade straight chain saturated fatty acid having18 carbon atoms in the alkyl chain, purity 95.0%

Oleic acid: First class grade straight chain unsaturated fatty acidhaving 18 carbon atoms in the alkyl chain, purity approximately 60.0%

Behenic acid: Straight chain saturated fatty acid having 22 carbon atomsin the alkyl chain, purity 99.0%

Benzoic acid: Special grade, purity 99.5%

Para-toluic acid: Special grade benzoic acid having a methyl group atthe p-position, purity 98.0%

Acetic acid: Special grade alkyl fatty acid having 2 carbon atoms,purity 99.7%

Propionic acid: Special grade alkyl fatty acid having 3 carbon atoms,purity 98.0%

Butyric acid: Special grade alkyl fatty acid having 4 carbon atoms,purity 98.0%

Formic acid: Special grade alkyl fatty acid having 1 carbon atom, purity98.0%

Base Oils A to D

Base oil A: Paraffin-based mineral oil obtained by dewaxing and solventrefining, group 1 base oil, kinematic viscosity 11.25 mm²/s at 100° C.,viscosity index 97.

Base oil B: Poly-α-olefin, group 4 base oil, kinematic viscosity 6.34mm²/s at 100° C., viscosity index 136.

Base oil C: Paraffin-based mineral oil produced by high levelhydrogenation refining, group 3 base oil, kinematic viscosity 7.603mm²/s at 100° C., viscosity index 128.

Base oil D: GTL (gas-to-liquid) synthesized by the Fischer Tropschmethod, group 3 base oil, kinematic viscosity 7.77 mm²/s at 100° C.,kinematic viscosity 43.88 mm²/s at 400° C., viscosity index 148.

Working Example 1

Base oil A as a raw material and stearic acid, acetic acid and benzoicacid were placed in a grease production tank and heated to 90° C. so asto melt the contents of the tank. Next, an appropriate quantity ofcalcium hydroxide dissolved or dispersed in advance in distilled waterwas introduced into the tank. Here, the fatty acids and the basiccalcium underwent a saponification reaction, thereby graduallygenerating a soap in the base oil, and this was then heated so as tocomplete dehydration and form a grease thickening agent. Followingcompletion of the dehydration, the temperature was increased to 200° C.,blending was effected through vigorous stirring, and the mixture wasthen allowed to return to room temperature. A homogeneous grease havinga No. 3 thickness was then obtained using a three-roll mill.

Working Example 2

Base oil A as a raw material and oleic acid, acetic acid and benzoicacid were placed in a grease production tank, and a homogeneous greasehaving a No. 2 thickness was obtained in the same way as in WorkingExample 1.

Working Example 3

Base oil A as a raw material and stearic acid, acetic acid andpara-toluic acid were placed in a grease production tank, and ahomogeneous grease having a No. 1.5 thickness was obtained in the sameway as in Working Example 1.

Working Example 4

Base oil A as a raw material and stearic acid, butyric acid and benzoicacid were placed in a grease production tank, and a homogeneous greasehaving a No. 2 thickness was obtained in the same way as in WorkingExample 1.

Working Example 5

Base oil A as a raw material and behenic acid, acetic acid and benzoicacid were placed in a grease production tank, and a homogeneous greasehaving a No. 3 thickness was obtained in the same way as in WorkingExample 1.

Working Example 6

Using the blending quantities shown for Working Example 5 in Table 1, ahomogeneous grease having a No. 0 thickness was obtained in the same wayas in Working Example 1.

Working Example 7

Using the blending quantities shown for Working Example 5 in Table 1, ahomogeneous grease having a No. 00 thickness was obtained in the sameway as in Working Example 1.

Working Example 8

Base oil B as a raw material and behenic acid, acetic acid and benzoicacid were placed in a grease production tank at the blending quantitiesshown for Working Example 6 in Table 1, and a homogeneous grease havinga No. 2 thickness was obtained in the same way as in Working Example 1.

Working Example 9

Base oil C as a raw material and stearic acid, acetic acid and benzoicacid were placed in a grease production tank at the blending quantitiesshown for Working Example 7 in Table 1, and a homogeneous grease havinga No. 2 thickness was obtained in the same way as in Working Example 1.

Working Example 10

Base oil D as a raw material and stearic acid, acetic acid and benzoicacid were placed in a grease production tank, and a homogeneous greasehaving a No. 2 thickness was obtained in the same way as in WorkingExample 1.

Working Example 11

A base oil obtained by blending base oils A, B, C and D as a rawmaterial and stearic acid, acetic acid and benzoic acid were placed in agrease production tank, and a homogeneous grease having a No. 2.5thickness was obtained in the same way as in Working Example 1.

Comparative Example 1

Base oil A as a raw material and stearic acid were placed in a greaseproduction tank and heated to 90° C. so as to melt the contents of thetank. Next, an appropriate quantity of calcium hydroxide dissolved ordispersed in advance in distilled water was introduced into the tank.Here, the fatty acid and the basic calcium underwent a saponificationreaction, thereby gradually generating a soap in the base oil, and thiswas then heated so as to complete dehydration and form a greasethickening agent. Following completion of the dehydration, thetemperature was increased to 130° C., blending was effected throughvigorous stirring, and the mixture was then allowed to return to roomtemperature. A homogeneous grease was then obtained using a three-rollmill.

Comparative Example 2

Base oil A as a raw material and stearic acid and acetic acid wereplaced in a grease production tank and heated to 90° C. so as to meltthe contents of the tank. Next, an appropriate quantity of calciumhydroxide dissolved or dispersed in advance in distilled water wasintroduced into the tank. Here, the fatty acids and the basic calciumunderwent a saponification reaction, thereby gradually generating a soapin the base oil, and this was then heated so as to complete dehydrationand form a grease thickening agent. Following completion of thedehydration, the temperature was increased to 200° C., blending waseffected through vigorous stirring, and the mixture was then allowed toreturn to room temperature. A homogeneous grease was then obtained usinga three-roll mill.

Comparative Example 3

Base oil A as a raw material and stearic acid and benzoic acid wereplaced in a grease production tank, and a grease was obtained usingsimilar blending quantities to those shown in the table in accordancewith the production method used in Comparative Example 2.

Comparative Example 4

Base oil A as a raw material and stearic acid, benzoic acid and formicacid were placed in a grease production tank, and a grease was obtainedusing similar blending quantities to those shown in the table inaccordance with the production method used in Comparative Example 2, butthe grease separated and produced a fluid substance.

Comparative Example 5

A commercially available lithium-based grease produced by Showa Shellwas used, lithium 12-hydroxystearate soap was used as a thickening agentand a mineral oil-based lubricating oil was used in a base oil, and theviscosity of the base oil was 12.2 mm²/s at 100° C.

The abovementioned results are shown in Table 1 and Table 2. Moreover,the “Not measurable” for Comparative Example 1 in Table 2 means that itwas not possible to obtain a precise measured value for the evaporationloss due to the grease composition becoming fluid and flowing away. Inaddition, the “Not measurable” for Comparative Example 4 means that thedropping point could not be measured because it was not possible toobtain a grease structure due to the base oil and the thickening agentseparating.

TABLE 1 Working Example 1 2 3 4 5 6 7 8 9 10 11 (a) Thickening agent(mass %) 3.99 3.99 4.33 3.57 4.32 2.16 1.30 4.32 3.99 3.99 3.99 AlkaliCalcium hydroxide Higher fatty acid Stearic acid 10.98 10.87 10.22 10.8810.88 10.88 Oleic acid 10.88 Behenic acid 9.66 4.83 2.89 9.66 Aromaticfatty acid Benzoic acid 1.00 1.00 2.69 1.95 0.98 0.59 1.95 1.00 1.001.00 Paratoluic acid 1.00 Lower fatty acid Acetic acid 3.48 3.48 3.423.42 1.71 1.03 3.42 3.48 3.48 3.48 Butyric acid 2.70 Formic acid Totalthickening agent 19.35 19.35 19.62 19.18 19.35 9.68 5.81 19.35 19.3519.35 19.35 (b) Base oil (mass %) 80.65 80.65 80.38 80.82 80.65 90.3294.19 20.65 Base oil A Base oil B 80.65 20.00 Base oil C 80.65 20.00Base oil D 80.65 20.00 Composition total (%) 100.00 100.00 100.00 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 Properties Colour PalePale Pale Pale Pale Pale Pale Pale Pale Pale Pale yellow yellow yellowyellow yellow yellow yellow white white white yellow State Grease GreaseGrease Grease Grease Grease Grease Grease Grease Grease Grease Qualityof texture ⊚ ⊚ ⊚ ◯ ◯ ◯ ◯ ◯ ⊚ ⊚ ⊚ Viscoelasticity (body strength) ⊚ ◯ ◯ Δ⊚ ⊚ Δ ⊚ ⊚ ⊚ ⊚ Ease of production (ease of dehydration ⊚ ◯ ◯ Δ ◯ ◯ ◯ ◯ ⊚⊚ ⊚ and so on) Thickness Worked penetration 247 288 307 271 212 374 408273 267 271 257 NLG thickness grade No. 3 No. 2 No. 1.5 No. 2 No. 3 No.0 No. 00 No. 2 No. 2 No. 2 No. 2.5 Dropping point ° C. >260 >260 >260211 >260 >260 241 >260 >260 >260 >260 Thin film heating Evaporation loss3.95 3.33 3.37 3.34 3.90 5.12 6.54 3.94 3.74 3.85 3.27 test (%) 150° C.,24 hours Observed grease Pale Pale Pale Pale Pale Pale Pale Pale PalePale Pale colour yellow yellow brown brown yellow yellow yellow yellowyellow yellow yellow

TABLE 2 Comparative Example 1 2 3 4 5 (a) Thickening agent (mass %) 1.163.99 2.25 4.35 Commercially Alkali Calcium hydroxide available Higherfatty acid Stearic acid 9.40 10.88 6.40 10.87 lithium grease Oleic acidBehenic acid Aromatic fatty acid Benzoic acid 2.74 1.00 Paratoluic acidLower fatty acid Acetic acid 3.48 Butyric acid Formic acid 3.19 Totalthickening agent 10.56 18.35 11.39 19.41 (b) Base oil (mass %) 89.4481.65 88.61 80.59 Base oil A Base oil B Base oil C Base oil DComposition total (%) 100.00 100.00 100.00 100.00 Properties Colour Paleyellow Pale yellow Pale yellow Pale yellow Pale brown State GreaseGrease Grease Separated Fluid Grease Quality of texture ◯ ◯ ◯ X ⊚Viscoelasticity (body strength) Δ Δ Δ X ◯ Ease of production (ease ofdehydration and so on) Δ Δ Δ X ⊚ Thickness Worked penetration 328 314349 — 273 NLG thickness grade No. 1 No. 1 No. 0.5 — No. 2 Dropping point(° C.) 108 170 114 Not measurable 185 Thin film heating test Evaporationloss (%) Not measurable 6.77 6.07 — 15.00 150° C., 24 hours Observedgrease colour Brown Pale brown Brown — Dark brown

As is clear from Table 1 and Table 2, Comparative Examples 1 and 2(grease compositions that did not contain an aromatic fatty acid) andComparative Example 3 (a grease composition that did not contain a lowerfatty acid) all had a low dropping point and did not exhibit heatresistance, Comparative Example 4 could not form a grease structure dueto the base oil and the thickening agent separating, and ComparativeExample 5 (a commercially available lithium grease) underwentsignificant evaporation loss and discolouration. However, the workingexamples according to the present invention all had dropping points inexcess of 200° C., had suitable thicknesses for greases, underwentlittle evaporation loss at high temperatures, exhibited excellentthermal stability and exhibited stable lubrication activity even inhigh-temperature regions.

That which is claimed is:
 1. A grease composition comprising: a base oiland a thickening agent comprising a calcium complex soap, wherein thecalcium complex soap comprises: (1) a calcium soap of a higher fattyacid present in an amount of 2 to 15 parts by mass, wherein the higherfatty acid is a substituted or unsubstituted straight chain highermono-fatty acid having 18 to 22 carbon atoms, (2) a calcium soap of anaromatic fatty acid present in an amount of 0.5 to 3 parts by mass,wherein the aromatic fatty acid is an aromatic mono-fatty acid having asubstituted or unsubstituted benzene ring and (3) a calcium soap of alower fatty acid present in an amount of 1 to 5 parts by mass, relativeto 100 parts by mass of the overall grease composition, wherein thelower fatty acid is a straight chain saturated lower mono-fatty acidhaving 2 to 4 carbon atoms wherein the amount of the higher fatty acid,relative to 100 parts by mass of the total fatty acid content, isgreater than the amount of the lower fatty acid.
 2. The greasecomposition according to claim 1, wherein the dropping point is at least180° C. or higher, as measured by JIS K 2220
 8. 3. The greasecomposition according to claim 1, wherein: the higher fatty acid isselected from the group consisting of: stearic acid, oleic acid,12-hydroxystearic acid, behenic acid, and a combination thereof, thearomatic fatty acid is selected from the group consisting of: benzoicacid, para-toluic acid, and a combination thereof, and the lower fattyacid is acetic acid.
 4. The grease composition of claim 1, wherein thedropping point is at least 250° C. or higher, as measured by JIS K
 22208. 5. The grease composition according to claim 1, wherein the higherfatty acid is selected from the group consisting of: stearic acid, oleicacid, 12-hydroxystearic acid, behenic acid, and a combination thereof.6. The grease composition according to claim 1, wherein the aromaticfatty acid is selected from the group consisting of: benzoic acid,para-toluic acid, and a combination thereof.
 7. The grease compositionaccording to claim 1, wherein the lower fatty acid is acetic acid. 8.The grease composition according to claim 1, wherein the base oil ispresent in an amount of 60 to 99 parts by mass, relative to 100 parts bymass of the overall grease composition.
 9. The grease compositionaccording to claim 1, wherein the calcium complex soap is present in anamount of 1 to 40 parts by mass, relative to 100 parts by mass of theoverall grease composition.
 10. A method for preparing a greasecomposition comprising: combining a base oil, calcium hydroxide, ahigher fatty acid, an aromatic fatty acid, and a lower fatty acid toform the grease composition wherein: (1) the higher fatty acid is asubstituted or unsubstituted straight chain higher mono-fatty acidhaving 18 to 22 carbon atoms present in an amount of 2 to 15 parts bymass, (2) the aromatic fatty acid is an aromatic mono-fatty acid havinga substituted or unsubstituted benzene ring present in an amount of 0.5to 3 parts by mass, and (3) the lower fatty is a straight chainsaturated lower mono-fatty acid having 2 to 4 carbon atoms present in anamount of 1 to 5 parts by mass, relative to 100 parts by mass of theoverall grease composition, wherein the amount of the higher fatty acid,relative to 100 parts by mass of the total fatty acid content, isgreater than the amount of the lower fatty acid.
 11. The methodaccording to claim 10, wherein the dropping point is at least 180° C. orhigher, as measured by JIS K 2220
 8. 12. The method according to claim10, wherein the dropping point is at least 250° C. or higher, asmeasured by JIS K 2220
 8. 13. The method according to claim 10, wherein:the higher fatty acid is selected from the group consisting of: stearicacid, oleic acid, 12-hydroxystearic acid, behenic acid, and acombination thereof, the aromatic fatty acid is selected from the groupconsisting of: benzoic acid, para-toluic acid, and a combinationthereof, and the lower fatty acid is acetic acid.
 14. The methodaccording to claim 10, wherein the base oil is present in an amount of60 to 99 parts by mass, relative to 100 parts by mass of the overallgrease composition.
 15. The method according to claim 10, wherein thecalcium complex soap is present in an amount of 1 to 40 parts by mass,relative to 100 parts by mass of the overall grease composition.
 16. Thegrease composition according to claim 1, wherein the higher fatty acidis present in an amount of 62 to 70 parts by mass, relative to 100 partsby mass of the total fatty acid content.
 17. The grease compositionaccording to claim 1, wherein the aromatic fatty acid is present in anamount of 2 to 17 parts by mass, relative to 100 parts by mass of thetotal fatty acid content.
 18. The grease composition according to claim1, wherein the lower fatty acid is present in an amount of 10 to 24parts by mass, relative to 100 parts by mass of the total fatty acidcontent.
 19. The method according to claim 10, wherein the higher fattyacid is present in an amount of 62 to 70 parts by mass, relative to 100parts by mass of the total fatty acid content.
 20. The method accordingto claim 10, wherein the aromatic fatty acid is present in an amount of2 to 17 parts by mass, relative to 100 parts by mass of the total fattyacid content.
 21. The method according to claim 10, wherein the lowerfatty acid is present in an amount of 10 to 24 parts by mass, relativeto 100 parts by mass of the total fatty acid content.